Wells drilled in low-permeability subterranean formations are often treated by reservoir stimulation techniques, such as hydraulic fracturing, to increase hydrocarbon production rate. High viscosity fluids may be employed to carry proppant down-hole to prop open fractures in the formation. Known linear gels (water containing a gelling agent without cross-linker) that can be operated at ambient temperature at the surface generally do not exhibit a sufficiently high viscosity to transfer proppant of a large size or large quantity. Consequently, cross-linkers may be used to increase fluid viscosity, providing adequate transport of larger proppant sizes or larger proppant quantity. Higher viscosity fluids also create wider fractures within the formation.
Guar and guar derivatives are among the most often used viscosifying agents, such as polymers, in hydraulic fracturing treatment. Guar derivatives, such as carboxymethyl guar (CMG) and carboxymethyl hydroxypropyl guar (CMHPG), are predominantly used in wells with a high bottom-hole temperature (BHT). Interest in cellulose derivatives, such as hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and carboxymethyl hydroxyethyl cellulose (CMHEC), has increased for fracturing treatment due to the natural abundance of cellulose.
Often, hydraulic fracturing gels include cross-linking delay additives, gel breakers, and fluid loss control additives among many other possible additives to adapt hydraulic fracturing gel to the circumstances of hydraulic fracturing. A variety of gelling agents and cross-linkers are known for use in hydraulic fracturing gel. For a delay additive, cross-linking reactions are so designed that viscosity development begins after placement of hydraulic fracturing gel deep within a well.
In a related manner, rheology modifiers, such as gel breakers, may be included in hydraulic fracturing gel to significantly decrease viscosity after fracturing for easier removal of the gel from the well. To the extent that the cross-linked gel contains a gel breaker, the gel breaker may be configured for delayed action to maintain desirable properties of the cross-linked gel while fracturing. Even so, additional rheology modifiers, such as gel breakers, are desired to provide an increased variety of options for interacting with viscosifying agents and related components.